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What is causing the recent rise in drug-resistant urinary tract infections?

Researchers claim that antibiotics used in industrial poultry farming are the vector by which resistant bacteria are spreading to humans.

The Atlantic has published a troubling article by science writer Maryn McKenna (“Superbug”) about the mysterious recent increase in the number of women — and some men — who are being diagnosed with antibiotic-resistant urinary tract infections (UTIs).

UTIs, which affect up to 8 million women in the United States each year, are most commonly caused by a form of intestinal bacterium E. coli known as ExPEC. (Women are affected more than men because they have a shorter urinary tract.) Since the advent of antibiotics, treatment has been easy and effective: a short-term bout of those drugs.

But within the past two or three years, reports McKenna, a growing number of physicians and their patients are finding that antibiotics are not working. That’s a serious problem, for untreated infections (or ones that don’t respond to drugs) can potentially spread to the kidneys and into the bloodstream, where they can be fatal.

Because there is no national registry for drug-resistant UTIs, the precise number of people who have developed them is unknown. But, says McKenna, drug-resistant UTIs “have become so common that last year the specialty society for infectious-disease physicians had to revise its recommendations for which drugs to prescribe.”

And the source of this newly resistant E. coli?  It’s been a mystery, writes McKenna,

except to a small group of researchers in several countries. They contend there is persuasive evidence that the bacteria are coming from poultry. More precisely, coming from poultry raised with the routine use of antibiotics, which takes in most of the 8.6 billion chickens raised for meat in the U.S. each year.

Their research in the United States, Canada, and Europe (published most recently this month, In June, and in March) has found close genetic matches between resistant E. coli collected from human patients and resistant strains found on chicken or turkey sold in supermarkets or collected from birds being slaughtered. The researchers contend that poultry — especially chicken, the low-cost, low-fat protein that Americans eat more than any other meat — is the bridge that allows resistant bacteria to move to humans, taking up residence in the body and sparking infections when conditions are right. Touching raw meat that contains the resistant bacteria, or coming into environmental contact with it — say, by eating lettuce that was cross-contaminated — are easy ways to become infected. …

The proposed link between resistant bacteria in chickens and those causing UTIs is not the first time researchers have traced connections between agricultural antibiotic use and human illness. But because the UTI epidemic is so large and costly, the assertion that it might be tied to chicken production has brought renewed attention to the issue.

Minnesota connections

McKenna’s story contains two Minnesota references. She mentions a 2005 study by University of Minnesota professor of medicine and infectious disease expert Dr. James R. Johnson, which found resistant E. coli strains that matched ones from human E. coli infections in retail meat bought in local supermarkets.

As a result of that study and similar ones conducted in Europe, Canada, and Wisconsin, “investigators began to sort out two things,” writes McKenna.

They became convinced that the resistance pattern could be traced back to animal antibiotic use, because resistance genes in the bacteria causing human infections matched genes found in bacteria on conventially raised meat. And they began to understand that E. coli’s complexity would make this new resistance problem a difficult one to solve.

The strains that cross to humans via poultry meat “don’t establish themselves as big, successful lineages” of bacteria that would be easy to target, Johnson said. “But collectively they can cause a lot of infections, because there are just so many of them and they’re so diverse.”

Dr. Randall SingerDr. Randall Singer

Not everybody agrees with the idea that chickens might be the source of antibiotic-resistant UTIs. One of the skeptics quoted in McKenna’s article is Dr. Randall Singer, who also studies infectious diseases and is an assistant professor of epidemiology at the University of Minnesota’s College of Veterinary Medicine.

“[He] points out,” writes McKenna, “that some recent research suggests that antibiotic resistance genes in E. coli may actually originate from humans, spreading through sewage into ground and surface waters, and from there into the environment and lifestock. The resistance found in human and poultry E. coli “is a typical multi-drug resistance pattern that you find all over the world, including in wild animal populations that have had no exposure to” humans, he said. “To say these genes exist in a person because of an antibiotic that was given to a chicken is too narrow an interpretation.”

You can read McKenna’s article in full on the Atlantic website. The article was produced in collaboration with the non-profit Food & Environmental Reporting Network.

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